In the art of tissue making, a deflection member may be used to imprint a tissue web against a Yankee dryer or other drying surface. Known deflection members include macroscopically monoplanar fabrics such as a through-drying fabric having a woven substrate and UV-cured resin elements above the substrate. The cured resin elements define deflection conduits into which a moist tissue web can be deflected during a through drying operation to create bulky domes offering softness and absorbency, while the portions of the web residing on the surface of the resin elements are pressed against the dryer surface to create a network of pattern densified areas offering strength.
In the scope of imprinting technology, it is also known to use a press nip for increased deformation of the web into an imprinting fabric, as disclosed by Ampulski et al. in U.S. Pat. No. 5,855,739, xe2x80x9cPressed Paper Web and Method of Making the Same,xe2x80x9d issued Jan. 5, 1999, and U.S. Pat. No. 5,897,745, xe2x80x9cMethod of Wet Pressing Tissue Paper,xe2x80x9d issued Apr. 27, 1999, both of which are herein incorporated by reference in a manner consistent herewith. A related concept is the use of a low permeability flexible film or web placed over a paper web as it resides on an imprinting or molding fabric, wherein the film helps in molding of the paper web when differential air pressure is applied, for it reduces air flow through the web and increases the pressure differential experienced by the web, as disclosed in U.S. Pat. No. 5,893,965, xe2x80x9cMethod of Making Paper Web Using Flexible Sheet of Material,xe2x80x9d issued to P. D. Trokhan and V. Vitenberg, Apr. 13, 1999, herein incorporated by reference in a manner consistent herewith. The flexible film or web has the potential to increase water removal from the web as well as increase the degree of molding against a textured fabric. It is likewise said that a compression nip in which moist tissue is pressed between an imprinting fabric and a press felt can cause enhanced deformation and molding of a tissue web. This technology is said to allow a tissue web to be created with multiple zones having different elevations and thicknesses or densities. Also related is U.S. Pat. No. 5,972,813 issued to O. Polat et al. issued Oct. 26, 1999, which discloses an impervious texturing web.
The technology for producing textured webs as described in the above-referenced Ampulski patents and other related references can be improved through the novel application of deflection members other than the traditional fabrics known for imprinting or through drying technology, yielding a variety of benefits such as but not limited to any one of better molding of the web, enhanced mechanical and absorbency properties, and textures not easily achieved heretofore. In one embodiment, such deflection members include fabrics having raised elements that contact the web and deflection conduits, wherein the deflection member comprises geometries and/or materials capable of creating asymmetrical domes, either through contact in a compression nip or by imprinting the web onto the Yankee dryer. In one embodiment, for example, raised elements and/or deflection conduits in a deflection member, when viewed in cross-sections taken in the machine direction or cross-direction of the fabric, display leading and trailing edges having different angles relative to the vertical axis and desirably at least one side that is curved. In a related embodiment, the walls of a deflection conduit viewed in a cross-sectional profile taken in the machine direction or cross-direction are not both parallel and straight, but may be curved or nonlinear or non-parallel.
A particular cross-section that can be sufficient in demonstrating asymmetry of a raised element or deflection conduit is the machine direction cross-section that passes through the longest span in the machine direction of the structure under scrutiny. For example, with diamond-shaped deflection conduits aligned with the machine direction, the longest span in the machine direction would be a line from one vertex to the opposing vertex. For cylindrical deflection conduits, the longest machine direction span would comprise the diameter of the cylinder. For raised elements in a continuous network, the vertical plane aligned in the machine direction should be sought that passes through the greatest continuous length of the raised element. If the raised elements are discrete polygons or other discrete shapes, the portion of that shape that gives the longest span in the machine direction can be used. Of course, it is possible for a deflection member to be designed to display a symmetrical shape along one particular cross-section while being substantially asymmetrical elsewhere. Thus, while asymmetry along the machine direction cross-section spanning the longest length of the element under scrutiny can be sufficient to establish asymmetry, failure to find asymmetry in that particular profile does not necessarily excise a deflection member from the scope of the present invention. Profiles along other paths may need to be considered as well.
In a related embodiment, isolated structures, which can be either deflection conduits or raised elements, have asymmetrical profiles in the cross direction, even when the geometry in the plan view appears symmetrical. In another related embodiment, the raised elements terminate in top surfaces that are curved, not simply straight and flat.
Deflection members of the present invention can include those with elastomeric components in the raised elements, those comprising asymmetrical geometries in the raised elements, those comprising two or more subsets of raised elements having different material properties or geometries, and other fabrics with novel construction and materials. The application of the deflection members of the present invention can, in some embodiments, further be improved through the addition of shear onto the paper web for better molding against the fabric, or through use of an impervious, flexible film on the side of the paper web not in contact with the deflection member to increase the molding due to air pressure differentials applied across the web. In the latter case, the flexible film may be smooth or comprise a texture, and optionally may comprise apertures to decrease the molding in selected regions or to provide pinholes for producing a selectively apertured tissue web.
As used herein, the term xe2x80x9cdeflection memberxe2x80x9d refers to a textured fabric having a web contacting surface comprising raised elements and having deflection conduits, such that the fabric is capable of imparting texture to a web when the web is pressed or urged against the deflection member, particularly when the web is moist (e.g., having a moisture content of 30% or above, more specifically about 60% or above, more specifically still about 70% or above, and most specifically from about 75% to about 90%, with an exemplary range of from about 30% to about 55%). The deflection member can impart texture to a web by serving as:
an imprinting fabric, wherein the fabric presses the web against a solid surface such as a Yankee dryer, to which the web typically remains attached until creped off by a doctor blade;
a textured press fabric, wherein the fabric is pressed against the web in a compressive nip, typically with one or more additional fabrics or deformable belts present in the nip;
a through drying fabric, wherein differential air pressure forces the web to deform against the texture the of fabric;
a transfer fabric, in which the web is transferred to the fabric over a vacuum shoe to cause the web to deform against the fabric, including conditions of differential velocity transfer in which the web travels to the fabric at a higher speed than the fabric; or
by serving in any combination of the above roles; or in other embodiments in which a force urges a fibrous web against the fabric under conditions capable of imparting texture to the web.
Deflection members can be formed from a variety of techniques known in the art, including patterned photocuring or radiation curing of polymer resins after application of the resin to a base fabric, laser drilling of a material to form a stand-alone fabric or a layer for a fabric having a reinforcing base fabric, rapid prototyping methods (including selective laser sintering, stereolithography, and room temperature vulcanization molding) with or without a reinforcing base fabric in place, molding, and so forth.
The deflection members of the present invention can be used to produce paper webs and other webs having novel geometrical structures or novel physical properties. For example, webs with asymmetrical domes can offer a variety of advantages such as unique tactile properties. In some embodiments, the dome may be more flexible or deformable for a soft feel. In other embodiments, tissue comprising asymmetrical domes can have bidirectional frictional properties, meaning that the frictional properties along a pathway (e.g., the machine direction or cross-direction) depend on the direction of travel (forwards or backwards along that path). Thus, a tissue may feel smooth when it brushes against the skin in one direction, but offer higher friction for cleaning when the direction is reversed.